The incidence rate of epithelial ovarian cancer varies substantially among various races and geographic areas, but few specific risk factors accounting for these differences have been elucidated. Recent studies suggest that aspects of lactose and galactose consumption and metabolism could be associated with the incidence of epithelial ovarian cancer. If causal, these associations would help to explain racial and geographic trends. As part of a doctoral dissertation project, a case-control study is proposed to evaluate the possible association between lactose and galactose consumption and metabolism and epithelial ovarian cancer. All Caucasian female residents of three Western Washington counties below the age of 75 years, who are diagnosed with Stage I epithelial ovarian cancer during the period January 1, 1989, to December 31, 1991, will be identified using the Cancer Surveillance System, a population-based tumor registry that has served Western Washington since 1974. Each case will be asked to identify a friend control who is matched to the case on age (within 10 years). Study subjects will complete a self-administered food-frequency questionnaire; will be interviewed in-person to obtain demographic, reproductive, and medical information; and will undergo an oral lactose challenge followed by collection of blood and urine samples. Biological samples will be assayed for several enzymes and intermediates of lactose and galactose metabolism in order to identify women who are lactase persistent or have relatively low activity of galactose-1-phosphate uridyltransferase, an enzyme important in the metabolism of galactose. Approximately 242 women are expected to participate, of whom 170 are expected to provide biological samples. The relative risk of ovarian cancer associated with lactose and galactose consumption and metabolism will be estimated using logistic regression.